The Apache Soap project is an implementation of the draft W3C protocol
by the same name. It is based on, and supersedes, the IBM SOAP4J
implementation.

From the draft W3C specification: SOAP is a lightweight protocol for
exchange of information in a decentralized, distributed environment. It
is an XML based protocol that consists of three parts: an envelope that
defines a framework for describing what is in a message and how to
process it, a set of encoding rules for expressing instances of
application-defined datatypes, and a convention for representing remote
procedure calls and responses.